U.S. patent number 4,018,959 [Application Number 05/639,273] was granted by the patent office on 1977-04-19 for corrugating adhesive compositions containing thermoplastic polymer, thermosetting resin, and starch.
This patent grant is currently assigned to National Starch and Chemical Corporation. Invention is credited to Paul R. Demko, Frank J. Washabaugh, Robert H. Williams.
United States Patent |
4,018,959 |
Demko , et al. |
April 19, 1977 |
Corrugating adhesive compositions containing thermoplastic polymer,
thermosetting resin, and starch
Abstract
Improved adhesive compositions useful in the manufacturing of
corrugated boards are disclosed; said compositions being comprised
of a mixture of: (a) a crosslinkable water dispersible polymer, (b)
an ungelatinized starch, (c) a urea-formaldehyde resin, (d) an
acidic metal salt, and (e) water.
Inventors: |
Demko; Paul R. (Edison, NJ),
Washabaugh; Frank J. (Titusville, NJ), Williams; Robert
H. (Piscataway, NJ) |
Assignee: |
National Starch and Chemical
Corporation (Bridgewater, NJ)
|
Family
ID: |
27065395 |
Appl.
No.: |
05/639,273 |
Filed: |
December 10, 1975 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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537174 |
Dec 30, 1974 |
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Current U.S.
Class: |
428/182; 524/52;
524/47 |
Current CPC
Class: |
C09J
103/02 (20130101); C09J 131/04 (20130101); C09J
133/062 (20130101); C09J 161/20 (20130101); C09J
103/02 (20130101); C09J 131/04 (20130101); C09J
133/062 (20130101); C09J 161/20 (20130101); C08K
3/24 (20130101); C08L 31/04 (20130101); C08L
3/02 (20130101); C08L 61/20 (20130101); C08K
3/24 (20130101); C08L 33/06 (20130101); C08L
3/02 (20130101); C08L 61/20 (20130101); C08K
3/24 (20130101); C08L 61/20 (20130101); C08L
3/02 (20130101); C08L 31/04 (20130101); C08L
33/06 (20130101); C08K 3/24 (20130101); C08L
3/02 (20130101); C08L 31/04 (20130101); C08L
33/06 (20130101); C08L 61/20 (20130101); C08L
31/04 (20130101); C08K 3/24 (20130101); C08L
33/06 (20130101); C08L 3/02 (20130101); C08L
61/20 (20130101); C08L 2666/02 (20130101); C08L
2666/54 (20130101); C08L 2666/02 (20130101); C08L
2666/54 (20130101); C08L 2666/02 (20130101); C08L
2666/54 (20130101); C08L 2666/04 (20130101); C08L
2666/54 (20130101); Y10T 428/24694 (20150115); C08L
2666/02 (20130101); C08L 2666/04 (20130101); C08L
2666/54 (20130101) |
Current International
Class: |
C09J
103/02 (20060101); C09J 131/00 (20060101); C09J
131/04 (20060101); C09J 133/06 (20060101); C09J
161/20 (20060101); C09J 161/00 (20060101); C09J
103/00 (20060101); C08L 3/00 (20060101); C08L
3/02 (20060101); C08L 61/00 (20060101); C08L
61/20 (20060101); B32B 003/28 (); C08L
003/02 () |
Field of
Search: |
;260/17.3 ;428/182 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Chem. Absts.: 80(1974):60707X, "Adhesive," Pascu et al. .
Chem. Absts.: 77(1972):20830p, "Adhesive-Structures," Klein. .
Chem. Absts.: 77(1972)166,461R, "Paper Coating Compositions,"
Kuehlkamp et al. .
Chem. Absts.: 71(1969):92871b, "Wall Paper Coating,"
Elgood..
|
Primary Examiner: Woodberry; Edward M.
Attorney, Agent or Firm: Graham; Thomas B.
Claims
We claim:
1. A corrugating adhesive composition capable of yielding dry films
which are characterized by their outstanding water resistance and
thermal stability; said adhesive composition comprising a mixture
of (a) a crosslinkable polymer in aqueous emulsion form selected
from the group consisting of vinyl acetate homopolymers, copolymers
of vinyl acetate with one or more ethylenically unsaturated
copolymerizable comonomers, and copolymers of C.sub.1 -C.sub.8
alkyl esters of acrylic and methacrylic acids with one or more
ethylenically unsaturated copolymerizable comonomers; (b) an
ungelatinized starch which is present in amount ranging from 0.5 to
6.0 times the amount of the resinous content of said polymer, (c) a
thermosetting resin selected from the group consisting of
dimethylol ethylene urea, dimethylol methoxy ethyl carbamate,
dimethylol isobutyl carbamate, dimethylol hydroxyethyl triazone,
methylated methylol melamine, melamine-formaldehyde, and
urea-formaldehyde; said thermosetting resin being present in an
amount ranging from about 0.1 to about 5.0% by weight, of the total
composition, (d) an acidic metal salt curing agent selected from
the group consisting of chromium nitrate, chromium perchlorate,
zirconium nitrate, aluminum chloride, zirconium oxychloride,
aluminum sulfate and aluminum nitrate; said acidic metal salt
curing agent being present in an amount ranging from about 0.1 to
about 2.0%, by weight, of the total composition, and (e) water;
said composition having a viscosity of from about 100 to 2500
cps.
2. The adhesive composition of claim 1 wherein said crosslinkable
polymer is polyvinyl acetate or copolymer of vinyl acetate with one
or more copolymerizable comonomers selected from the group
consisting of (1) alpha-beta unsaturated mono and dicarboxylic
acids containing from 3 - 6 carton atoms, (2) alkyl esters of
acrylic and methacrylic acids wherein the alkyl group contains from
1 to 8 carbon atoms, (3) mono- or dialkyl esters of alpha, beta
unsaturated dicarboxylic acids wherein said acids contain from 3 to
6 carbon atoms, and the alkyl groups contain from 1 to 8 carbon
atoms, (4) vinyl halides, and (5) amides of acrylic and methacrylic
acids and their N-alkylol derivatives; said vinyl acetate being
present in an amount of at least 50%, by weight, of the
copolymer.
3. The adhesive composition of claim 1 wherein said crosslinkable
polymer is a copolymer of an alkyl (C.sub.1 -C.sub.8) ester of
acrylic or methacrylic acid with one or more copolymerizable
comonomers selected from the group consisting of amides of acrylic
or methacrylic acid; N-alkylol amides of acrylic or methacrylic
acid, cyanoethylacrylamide; and acrylonitrile; said alkyl ester of
acrylic or methacrylic acid being present in an amount of at least
60%, by weight, of the copolymer.
4. An adhesive composition comprising a copolymer of vinyl acetate
and N-methylol acrylamide having at least 50%, by weight, of vinyl
acetate; from 1.0 to 4.0 times the weight of the resinous content
of said copolymer of ungelatinized corn starch; from about 0.1 to
about 5.0%, by weight, of the total composition of a thermosetting
resin selected from the group consisting of dimethylol ethylene
urea, dimethylol hydroxyethyl triazone, dimethylol methoxy ethyl
carbamate, dimethylol isobutyl carbamate, methylated methylol
melamine, melamine-formaldehyde, and urea-formaldehyde, from about
0.1 to about 2.0%, by weight, of the total composition of an acidic
metal salt curing agent selected from the group consisting of
chromium nitrate, chromium perchlorate, zirconium nitrate, aluminum
nitrate, zirconium oxychloride, aluminum sulfate and aluminum
chloride; and water; said copolymer being in aqueous emulsion form
and said composition having a viscosity of from about 200 to 1400
cps.
5. The adhesive composition of claim 4 wherein said copolymer is
replaced with polyvinyl acetate.
6. The adhesive composition of claim 4 wherein said corn starch is
replaced with an ungelatinized waxy maize.
7. The adhesive composition of claim 4 wherein said copolymer is
replaced with a copolymer of butyl acrylate, vinyl acetate and
N-isobutoxy methylol acrylamide; said butyl acrylate being present
in an amount of at least 60%, by weight, of the total
copolymer.
8. The adhesive composition of claim 4 wherein said copolymer is
replaced with a copolymer of butyl acrylate, acrylonitrile, and
N-methylol acrylamide; said butyl acrylate being present in an
amount of at least 60%, by weight, of the total copolymer.
9. A corrugated paperboard product prepared employing the adhesive
composition of claim 1.
10. A corrugated paperboard product prepared employing the adhesive
composition of claim 5.
11. A corrugated paperboard product prepared employing the adhesive
composition of claim 7.
12. A corrugated paperboard product prepared employing the adhesive
composition of claim 8.
Description
This invention relates to improved adhesive compositions useful in
the manufacture of corrugated board. Said compositions are
characterized by their ability to form highly water-resistant bonds
which are capable of remaining stable and, in fact, become even
more water-resistant when subjected to the higher levels of
moisture and temperatures called for in "rigid-when-wet" processing
of the corrugated board.
The procedures employed in the production of corrugated board
normally involve a continuous process wherein a strip of paperboard
is first corrugated by means of heated, fluted rolls. An adhesive
is applied to the protruding tips on one side of this corrugated
strip and a flat sheet of paperboard, referred to as a liner, is
then brought into contact with these tips and, by the application
of heat and pressure, a bond is subsequently formed. The product
thus prepared is known as a single faced board inasmuch as it has a
liner on only one surface thereof. However, by repeating the above
described bonding process on the exposed side of the corrugated
strip of the single faced board, there is then produced so-called
double faced board comprising an inner corrugated layer sandwiched
between two liners.
In the production of corrugated board, it is often necessary to
render the corrugated board acceptable for use as containers
employed in high moisture environment applications. Conventional
method designed for this purpose usually involve treating or
impregnating at least one of the components or the entire assembly
with a moisture repellent mixture. Such methods usually call for
higher temperatures ranging from about 250.degree. to about
450.degree. F. Therefore, in order to obtain a finished corrugated
board which displays the desired "rigid-when-wet" properties, it is
necessary that the adhesive bonds therein remain intact throughout
the subsequent treatment with the moisture repellent mixture, i.e.
waterproof (water-resistant) and thermally stable.
It is well known to those skilled in the art that starch based and
silicate based adhesives are widely used in the corrugated board
industry. It is also well known that the water-resistance of such
adhesives may be limitedly enhanced by the addition thereto of
certain chemical modifiers. Nevertheless, as the demand for
rigid-when-wet corrugated fiberboard increases, practitioners have
encountered considerable difficulty in their efforts to provide a
corrugating adhesive which produces bonds which are capable of
remaining water resistant and thermally stable during the
subsequent processing of the corrugated board.
Heretofore, various procedures have been devised to produce
potentially waterproof, corrugating adhesive compositions. One of
such procedures involves combining an amylaceous material with
urea-formaldehyde resins and aluminum sulfate as a catalyst. The
bonds of the corrugated boards prepared from these adhesives
display some improved water resistance. However, the low pH levels
(less than 5.0) called for in such systems impart undesirable rate
and flow properties to the adhesive compositions, thus resulting in
greatly reduced machine speeds.
Other waterproofing corrugating adhesive such as those employing
resorcinol and formaldehyde with starch are plagued with, in
addition to the costliness of the resorcinol, shortcomings such as
the slow rate of the bond formation resulting from the
incompatibility of the starch based adhesive with the borax added
as a tackifying agent.
Still other waterproofing corrugating adhesives employ a product of
acetone with urea or with formaldehyde as the water-proofing agent.
Particular shortcomings of these adhesives are their relatively
shorter storage lives and concomitant, rapid loss of other
desirable characteristics.
Also, of particular concern is the inability of many compositions
of the prior art, such as those which consist mostly of
thermoplastic materials, to display the desired heat resistance and
rapid tack buildup called for by currently utilized corrugators. It
is due to their thermoplasticity that these materials become less
heat stable and essentially gummy at low speeds, and tend to form
deposits on the machine which require frequent shut-downs for
cleanup.
Hence, it becomes obvious that a need exists for a corrugating
adhesive which is capable of overcoming the aforementioned problems
without offsetting any desired characteristics or properties.
It is, thus, the prime object of this invention to provide
corrugating adhesive compositions which are characterized by their
ability to produce highly water-resistant and thermally stable
bonds. It is a further object of this invention to provide adhesive
compositions useful in the production of corrugated board which is
intended to be subsequently processed for use a rigid-when-wet
boxboard material. Still other objects and advantages of this
invention will become apparent from the following description
thereof.
SUMMARY OF THE INVENTION
We have now found that corrugating adhesives capable of overcoming
the problems of the prior art discussed above can be prepared. More
particularly, we have found that corrugating adhesive compositions
capable of producing highly water-resistant and thermally stable
bonds may be prepared by mixing (a) a crosslinkable polymer
selected from the group consisting of vinyl acetate homopolymers;
copolymers of vinyl acetate with one or more ethylenically
unsaturated comonomers; and copolymers of C.sub.1 -C.sub.8 alkyl
esters of acrylic and methacrylic acids, and one or more
ethylenically unsathurated comonomers; (b) ungelatinized starch;
(c) a urea-formaldehyde resin or melamine-formaldehyde resin; (d)
an acidic metal salt curing agent; and (e) water. The compositions
are characterized by their ability to form stable water-resistant
bonds.
Briefly, in the preparation of our novel adhesive compositions it
is essential that, in all cases, the amount of ungelatinized starch
utilized be from about 0.5 to 6.0 times the amount of the resinous
solid content of the particular polymer and, that said compositions
have a viscosity within the prescribed range of about 100 to 2,500
cps. and preferably, about 200 to 1,400 cps. Compositions having a
viscosity above 1,400 cps. are too viscous to be utilized at top
machined speeds. Compositions having a viscosity above 2,500 cps.
can be used only at lower machine speeds, mainly because of poor
adhesive transfer and adhesive build-up on the paper guides of the
corrugator.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The polymers useful in the practice of this invention are in all
instances water dispersible and crosslinkable, i.e.,
self-crosslinking or capable of being crosslinked externally with a
thermosetting resin, used in aqueous-emulsion form. Among the
useful polymers are included homopolymers of vinyl acetate;
copolymers of vinyl acetate with one or more copolymerizable
comonomers, such as for example, (1) alkyl esters of acrylic and
methacrylic acids wherein the alkyl group contains from 1 to 8
carbon atoms, e.g. methyl acrylate, methyl methacrylate, ethyl
acrylate, ethyl methacrylate, butyl acrylate, etc.; (2) mono- or
dialkyl esters of alpha-, beta-unsaturated dicarboxylic acids
having 3 - 6 carbon atoms, wherein the alkyl group(s) contains from
1 to 8 carbon atoms, such as monoethyl maleate, dimethyl maleate,
dibutyl maleate, etc., as well as the corresponding fumarates,
itaconates, and citraconates; (3) alpha-, beta-unsaturated mono and
dicarboxylic acids having 3 - 6 carbon atoms such as crotonic,
acrylic, methacrylic, maleic, itaconic, and citraconic acids; (4)
vinyl halides such as vinyl chloride; and (5) amides of alpha-,
beta-unsaturated carboxylic acids and their N-alkylol derivatives
such as acrylamide and N-methylol acrylamide. It is preferred that
the total comonomer concentration should not exceed about 50%, by
weight, of the resulting polymer.
Other polymers useful in the practice of this invention are based
on alkyl esters of acrylic or methacrylic acids, wherein the alkyl
group contains 1 to 8 carbon atoms, copolymerized with one or more
copolymerizable comonomers such as amides of alpha-,
beta-unsaturated carboxylic acids and their N-alkylol derivatives
such as acrylamides and N-methylol acrylamide, N-isobutoxymethylol
acrylamide, cyanoethylacrylamide, and acrylonitrile. It is
preferred that said polymers based on alkyl esters of acrylic or
methacrylic acid will contain more than about 60% of the particular
acrylate ester.
In actually preparing these polymers, the practitioner may employ
any of the aqueous emulsion polymerization techniques well known to
those skilled in the art. These techniques generally involve the
reaction of an aqueous emulsion of the respective monomers in the
presence of a free radical type catalyst and, at times, other
ingredients. Although various colloids such as hydroxyethyl
cellulose, polymethylvinyl ether/maleic anhydride, polyacrylamide
and the like may be used, it is preferred that polyvinyl alcohol is
employed as the sole emulsifying agent in those preparations
wherein vinyl acetate is involved. In those preparations in which
vinyl acetate is not employed, surfactants such as sodium lauryl
sulfate, alkyl aryl sulfonates and the like may be used as the
emulsifying agent. Non-volatile buffers or salts are preferably
omitted so as to eliminate the presence of any fixed basic salts
which would ordinarily retard the crosslinking of the resulting
polymers.
The term "ungelatinized starch" is intended to include any type
starch, native or converted, which has not been placed in an
aqueous medium and heated or chemically modified to a point at
which the micellar network within the granules become so weakened
as to allow further hydration and irreversible granular swelling.
Suitable starches include, for example, those derived from corn,
potato, amioca, rice sago, tapioca, waxy maize, sorghum, wheat, and
the various derivatives of said starches. Hence, among the suitable
starches are included the various starch derivatives such as
ethers, esters, thin boiling types prepared by known processes such
as mild acid treatments, oxidative, etc. and those derivatives of
said starches which have high amylose contents, i.e., 50% or more
by weight, of amylose. Furthermore, it is possible in the practice
of this invention to employ a granular starch of which a small
portion has been partially swelled by any known means or
homogenized by subjecting it to shear. Therefore, our term
"ungelatinized starch" is seen to include any amylaceous material
which has not lost its granular polarization crosses and is capable
of swelling.
As previously mentioned, it is critical in the practice of this
invention that the ungelatinized starch component be employed in a
range from about 0.5 to about 6.0, preferably from 1.0 to 4.0,
times that amount of the resinous portion of the copolymer (based
on the weight of the total dry solid content).
As previously indicated, it is of great importance that the
adhesive compositions of this invention also contain an amount of
urea-formaldehyde or melamine-formaldehyde thermosetting resin.
Said thermosetting resin is utilized in an amount ranging from
about 0.1 to about 5.0 percent, by weight, of the total
composition. Among the various types of compounds useful in this
capacity are included dimethylol ethylene urea, dimethylol methoxy
ethyl carbamate, dimethylol hydroxyethyl triazone, dimethylol
isobutyl carbamate, methylated methylol melamine,
melamine-formaldehyde, and urea-formaldehyde. These compounds and
others which fall in either of the aforementioned classes of
thermosetting resins are usually commercially available. In the
practice of this invention, it is preferred that the adhesive
compositions contain from about 0.2 to about 5 percent, by weight,
of the total adhesive composition of dimethylol hydroxyethyl
traizone or a high molecular weight urea-formaldehyde resin.
In addition to the foregoing components, it is also required that
acidic metal salt curing agents be utilized in the above described
blends. The primary function of these curing agents is to cure
(crosslink) the polymer or films derived from the adhesive
compositions of this invention as well as enhance certain
properties thereof such as their water resistance. The acidic
nature of these agents also serves to accelerate the curing
process.
The preferred curing agents for use in the adhesive compositions of
this invention comprise acidic metal salts selected from the group
consisting of chromium nitrate, chromium perchlorate, zirconium
nitrate, zirconium nitrate, zirconium oxychloride, aluminum
chloride, and aluminum nitrate. These curing agents may be added
separately to the mixture of the starch slurry and the admixture of
the polymer and the thermosetting resin, or may first be added to
the starch slurry prior to its incorporation with said mixture.
They may be added in either manner at the time the adhesive
formulations are to be utilized, or if added earlier, they should
not be introduced any more than about 48 hours prior to such
utilization. The use of these acidic metal salts results in
improved water resistance to a far greater degree than is possible
with the use of the corresponding free acids.
It is preferred that said curing agents be utilized in an amount of
from 0.1 to 2.0%, by weight, of the total adhesive composition.
The adhesive compositions of this invention should be formulated
and thoroughyl blended as described above and thereafter applied,
as a homogeneous dispersion, to the fiberboard by means of a
corrugating machine.
Those skilled in the art will appreciate that when utilizing the
multi-step, single operation corrugating machines of today,
considerably higher temperatures of from about 320.degree. to
450.degree. F. are called for at the points at which the adhesive
is applied to the flutes. Therefor, since our novel adhesives are
thermosetting compositions which are cured, i.e., are crosslinked,
upon exposure to temperatures between from about 40.degree. to
252.degree. F., they may be utilized on the various corrugators now
widely employed throughout the industry, particularly those which
call for the use of thermosetting-resinous adhesives. Despite the
quite extensive degree of curing and concomitant improvements in
water resistance and stability resulting from the mere application
of the adhesive by the corrugator, the practitioner may prefer that
the substantially cured adhesive be even further heated to
completely cure said adhesive and thereby obtain most unusually
outstanding water-resistance and stability. Such results would be
realized in the case of a post-corrugation, rigid-when wet
treatment wherein the further curing of the adhesive is an
incidental effect of the heat required to thermoset a
rigid-when-wet application.
If desired, conventional non-chemically functional additives may be
incorporated into the novel adhesive compositions of this
invention. Among these additives may be included: fillers such as
finely ground polymers; thickeners such as inorganic colloidal
clays, polyvinyl alcohol, organic compounds such as acrylic acid,
polymers of ethylene oxide and the like; pigments such as titanium
dioxide, barium sulphate, and the like; and dyes, preferably
transparent, such as Brilliant Violet B, Fast Red 8 BLX, etc.
As previously indicated, the novel adhesive compositions of this
invention are preferably prepared just prior to being applied to
the fiberboard, usually to the flutes, by means of a conventional
corrugating machine. Said compositions have a solid content of from
about 25 to about 50 percent, preferably 40 to 43, by weight, of
the total composition. Notwithstanding the rheological properties
of the specific adhesive composition and the capability of the
particular corrugator, the novel compositions disclosed herein may
be applied in an amount to yield a dried weight of from about 0.5
to about 8.0 pounds per 1000 sq. ft. per two glue lines at a rate
ranging from about 50 to about 700 fpm. At the time of application,
said adhesive compositions are not sticky but become so shortly
thereafter when they are substantially cured by the heat emitted
from the machine, i.e., the steam applied to the double-backer hot
plates or the corrugating rolls of the single facer.
The adhesive compositions herein are widely useful in various well
known corrugating processes. Since they are capable of producing
excellent bonds at high temperatures, unlike the so called "cold
set" starch-free adhesives, they may be utilized on both single
facer and double facer stations. Furthermore, these compositions
are useful in the preparation of corrugated boxboards from which
containers designed to be utilized under special conditions are
made. Examples of such boxboard are those of the rigid-when-wet
type which are usually prepared by the combined or sequential
chemical and thermal processing of the corrugated board. It is the
unexpected ability of our compositions to withstand considerably
high temperatures for prolonged periods, e.g. between 200.degree.
and 400.degree. F. over considerable periods which accounts for
their wide usefulness. These and other advantages will become
apparent from the following examples, with further illustrate, but
do not limit, the scope of this invention. In these examples, all
amounts are in terms of parts by weight, unless otherwise
specified.
EXAMPLE I
This example illustrates the preparation of an adhesive composition
typical of this invention using two optional ingredients. This
example also illustrates the excellent properties of said adhesive
composition when utilized in the manufacturing of corrugated
boards.
The formulation of the adhesive was as follows:
______________________________________ Ingredient Amount
______________________________________ Water 4,500 ml A
commercially available colloidal clay 200 g Waxy maize 4,000 g
Chromium nitrate (44% aqueous solution) 200 ml Vinyl
acetate/N-methylol acrylamide, 4,000 g (96:4 wt. ratio) (aqueous
emulsion about 40% solids) Boric acid 20 g A commercial, high MW
urea-formaldehyde resin 400 g
______________________________________
The above described ingredients were throughly stirred into a
homogeneous adhesive composition which had a viscosity of 400 cps,
determined by means of a Brookfield Viscometer equipped with an RVF
No. 2 spindle at 20 rpm. Said composition was then utilized in the
manufacturing of standard type corrugated boards, in the manner set
forth below.
CORRUGATION
Several sample of single face, A-fluted corrugated boards were
prepared by means of a conventional type corrugator similar to
those employed in the industry. The A-fluted corrugated mediums
consisted of a commercially available wet strength fiberboard which
had a basis weight of 30 pounds per 1000 sq. ft., and the liner
boards consisted of a commercially available wet strength
fiberboard having a basis weight of 62 pounds per 1000 sq. ft. The
several samples of corrugated boards were each made at one of five
varied machine speeds ranging from 50 to 420 feet per minutes
(hereinafter fpm). Both the medium and the liner were preheated by
the various rolls over which they were passed prior to the
application of the adhesive between the lower corrugator roll and
the pressure roll. The average temperature of the latter rolls and
said various rolls was about 350.degree. F. In addition to being
preheated in the aforementioned manner, the medium was impinged
with steam to facilitate fluting. The metering gap on the glue
roll, through which the adhesive was dispensed, was set at 0.012
inches. This setting allowed for a coating weight on the 7 inch
wide board samples equivalent to about 1.5 pounds per 1000 sq. ft.
Upon completion of the corrugating operations, the resultant
corrugated boards were stored for about 24 hours under ambient
conditions, and then tested as described below.
PIN ADHESION TESTING
Duplicate 2 .times. 4 inch samples of each of the boards obtained
at each of five varied machine speeds were cut and thereafter
subjected to one of three especially designed adhesion tests. In
each of said tests, the actual method utilized to determine the
results was based on that of the TAPPI Standard UM 802 (formerly R
337) Pin Adhesion Test, using a conventional testing apparatus
obtainable from Testing Machines Inc., Mineola, Long Island, New
York. The test results were recorded in terms of pounds per
specimen area required to completely separate the fluted medium
from the liner.
The descriptions of the three particular tests, the five varied
speeds at which the corrugator was run, and the average of the two
corresponding test results respectively obtained in the
aforementioned manner are set forth in the table below. In this set
of results and in all those reported hereinafter, the highest
values represent the best results.
Table No. 1 ______________________________________ Description of
Tests and Results "Oven Cured" Wet Pin: tested after being dipped
in Wet Pin: water, placed in oven set at tested after 250.degree.
F., for 20 min., held Machine Dry Pin: 1 hour under ambient
conditions, for Speed tested immersion in 24 hours, and immersed in
(fpm) as is water water for 1 hour
______________________________________ 50 105 27 32 150 140 43 57
250 127 41 55 350 90 26 56 420 120 27 50
______________________________________
As indicated by the results obtained in each of the above described
tests, the resulting bonds produced by the adhesive composition
were unusually water resistant and highly, thermally stable. These
excellent properties displayed throughout the series of tests were
especially noted in those cases wherein the adhesive bonds of the
test samples were completely cured by placing them in the oven.
When an additional set of duplicate samples were tested in a manner
similar to that of the procedure described above, but with a 5 hour
holding time in the oven, the results were comparable to those
respectively obtained wherein the oven holding time was only 20
minutes.
EXAMPLE II
This example further illustrates the preparation of our novel
adhesive composition using three optional ingredients. This example
also illustrates the improved properties of said composition over
those of a composition similar to an adhesive which is widely
utilized in the corrugated box and board industry.
The adhesive was prepared by means of a two-step preparation as
follows:
Step I -- A thermosetting resinous mixture was first prepared by
admixing about 60.0 parts of a vinyl acetate:N-methylolacrylamide
copolymer (as described in Example I) and about 7 parts of a
commercially available, high molecular weight urea-formaldehyde
resin with about 30 parts of water which contained about 3.0 parts
of dissolved polyvinyl alcohol, and about 1.32 parts of a
commercially available defoaming agent. The foregoing ingredients
were moderately stirred for about 10 minutes, whereupon a
homogeneous mixture was formed.
Step II -- A suspension comprising 66.0 parts of water, 60.0 parts
of raw corn starch, and 3.0 parts of zirconium oxychloride (33%
aqueous solution) was admixed with the homogeneous mixture prepared
in Step I.
In this case, the starch to polymer resin solids ratio was about
2.5:1. The viscosity of the resulting adhesive composition, as
determined by the means described in Example I, was 620 cps. Said
composition was stored under ambient conditions for 24 hours, and
then utilized in the manufacturing of corrugated boards which were
to be subsequently compared with boards made using an adhesive
composition similar to that widely utilized in the corrugated box
and board industry.
The adhesive composition utilized herein as a control essentially
consisted of a conventional starch based carrier and a resinous
secondary combination. Said carrier comprised an aqueous dispersion
of gelatinized starch in which the gelatinization had been induced
by caustic soda. The resinous secondary combination comprised a
mixture of an aqueous suspension of granular corn starch, an
aqueous emulsion of about 3.5:1 of a vinyl acetate and dibutyl
maleate copolymer and vinyl acetate homopolymer. The ratio of the
total starch content to the total resin content of the control
composition was about 2.3:1. The viscosity of said control,
determined in the same manner as that used for the sample, was 600
cps.
The two adhesive compositions described above were then each
utilized in the manufacturing of a series of five corrugated boards
in the manner described in Example I. In all cases, the medium and
the liner were similar to those respectively employed in Example I.
The resulting boards were held under ambient conditions for 24
hours, and the adhesive bonds thereof were then tested for their
ability to remain intact in the presence of water and heat. The
test methods utilized herein were the same as those outlined in
Example I, except the oven temperature in the "Oven Cured" Wet Pin
test was maintained at 350.degree. F.
The averages of the two corresponding test results respectively
obtained for each of the varied speeds, by the three test methods
are presented below in Table No. 2.
Table No. 2
__________________________________________________________________________
Test Machine Speed (fpm) Test Adhesive Control
__________________________________________________________________________
Dry Pin: 50 113.0 83.0 150 168.0 118.0 250 167.5 no adhesion 350
145.0 no adhesion 420 147.0 no adhesion Wet Pin: 50 13.5 11.0 150
33.0 15.5 250 35.0 no adhesion 350 18.0 no adhesion 420 13.5 no
adhesion "Oven Cured" 50 29.0 20.0 Wet Pin: 150 51.0 34.0 250 62.0
no adhesion 350 72.0 no adhesion 420 66.0 no adhesion
__________________________________________________________________________
The data presented above clearly shows the unusually greater water
resistance of the test adhesive composition over the control. The
superiority of the test adhesive is consistently reflected by the
better results obtained throughout the entire series of tests. As
indicated by the absence of any measurable results, the control
adhesive was unable to produce a stable bond at machine speeds in
excess of 150 fpm.
EXAMPLES III - V
These examples illustrate the usefulness of various granular
starches in the preparation of adhesive compositions typical of
this invention.
Each of three test adhesives designated A, B, and C, were prepared
by means of the two step procedure outlined in Example I, utilizing
0.5%, by weight, of chromium nitrate based on the weight of the
total adhesive composition (total solids plus water) in place of
the zirconium oxychloride. In all three cases, the starch to resin
ratio was approximately 2:1. The particular starches respectively
employed were raw corn starch in sample A, waxy maize in sample B,
and raw wheat starch in sample C. The viscosities of the thusly
prepared adhesive compositions, as determined by means of the
method described in Example I were 600 cps, 900 cps, and 880 cps,
respectively. Each of said compositions was then utilized in the
manufacturing of a series of A-fluted, single face corrugated
boards, at varied machine speeds, in a manner similar to that set
forth in Example I. The resulting boards were held under ambient
conditions for 24 hours, and then each of three sets of 2 .times. 4
inch duplicate samples taken from each board was tested by the
means employed in Example II. The test results are presented below
in Table No. 3.
Table No. 3
__________________________________________________________________________
Sample Identification Test Machine Speed (fpm) A B C
__________________________________________________________________________
50 144 150 (36.5 150 179.5 179 167.5 Dry Pin 250 169.5 177.5 168
350 164 162.5 150 420 140 158 155 50 31 23.5 33.5 150 41.5 29.0
47.0 Wet Pin 250 48.5 31.0 42.5 350 56.5 37.0 38.5 420 56.0 53.0
44.0 50 42.0 36.5 43.0 150 72.0 56.0 54.5 "Oven" Cured 250 88.0
60.0 54.5 Wet Pin 350 90.0 63.5 78.5 420 68.0 83.5 78.0
__________________________________________________________________________
EXAMPLE VI
This example further illustrates the preparation of an adhesive
composition typical of this invention and, the thermal stability
and water resistance of said composition.
To make the adhesive composition, in this case, Example II was
repeated, using about 1.75 parts of aluminum chloride in lieu of
the zirconium oxychloride. The resultant composition had a
viscosity of 620 cps, as determined in the above described
manner.
Portions of the immediately described composition were utilized in
the preparation of a series of five, single face corrugated boards,
at varied machine speeds. The resultant boards were held for 24
hours under ambient conditions, and then the bonds of duplicate
samples taken from each of said boards were tested by the three
methods described hereinabove. The varied speeds at which the
corrugations were carried out and the average of the respective
tests results were as follows:
______________________________________ Machine "Oven Cured" Speed
(fpm) Dry Pin Wet Pin Wet Pin
______________________________________ 50 142.5 28.0 38.0 150 168.5
43.0 53.0 250 164.5 35.0 72.0 350 172.5 57.0 75.5 420 163.5 56.0
72.5 ______________________________________
The data presented above clearly shows the unusually outstanding
thermal stability and water resistance of the present composition
wherein an aluminum chloride and urea-formaldehyde combination is
employed.
EXAMPLES VII - X
These examples illustrate the use of different amounts of starch in
additional adhesive compositions typical of this invention and, the
water resistance and thermal stability of said compositions.
Each of six test adhesive compositions, D - I, were prepared using
the ingredients and method set forth in Example II, using a varied
amount of corn starch with chromium nitrate, in lieu of the
zirconium oxychloride. In each of the preparations, the amount of
chromium nitrate utilized was about 0.5%, by weight, of the total
composition.
Portions of each of the compositions described above were utilized
in the manufacturing of five single face-corrugated boards, at
varied machine speeds by the method outlined in Example I. The
resulting boards were then stored under ambient conditions for 24
hours. Thereafter three sets of duplicate 2 .times. 4 inch samples
cut from said boards were each subjected to the Pin Adhesion tests
described in Example II.
The ratio of starch to resinous solids of the copolymer,
corresponding viscosities, and the averaged test results are set
forth below in Table No. 4.
Table No. 4
__________________________________________________________________________
TEST Results Starch: Machine "Oven Sam- Copolymer Viscosity Speed
Cured" ple Solids (cps) (fpm) Dry Pin Wet Pin Wet Pin
__________________________________________________________________________
D 0.5:1.0 480 50 99.0 32.0 30.5 150 178.5 48.5 67.5 250 194.5 61.0
81.0 350 181.5 75.0 92.5 420 183.0 72.0 92.5 E 1.0:1.0 850 50 163.5
38.5 37.5 150 189.0 55.0 69.5 250 184.0 66.5 86.5 350 201.5 69.5
87.5 420 196.0 70.5 86.0 F 3.0:1.0 240 50 107.0 16.0 23.5 150 156.0
33.0 46.0 250 180.5 40.0 60.5 350 169.5 36.5 77.0 420 172.0 41.0
76.0 G 4.0:1.0 260 50 93.0 13.5 15.5 150 156.0 26.0 38.5 250 166.0
31.0 52.0 350 155.5 25.0 62.0 420 169.5 30.5 70.5 H 5.0:1.0 280 50
122.5 13.5 20.5 150 156.0 16.5 35.0 250 151.5 17.5 40.0 350 132.0
12.0 34.0 420 121.0 8.5 28.5 I 6.0:1.0 320 50 134.0 11.0 20.5 150
150.5 12.0 25.0 250 150.0 8.5 36.5 350 140.0 5.5 3.5 420 98.5 2.5
--
__________________________________________________________________________
Based on the results presented above, it becomes apparent that the
amount of ungelatinized starch utilized in preparing the adhesive
compositions of this invention may be varied over a wide range. The
outstanding water resistance and thermal stability characteristics
of such compositions are shown by the excellent results
consistently obtained throughout the series of tests.
EXAMPLES XI -- XII
These examples illustrate the usefulness of additional acid salt
curing agents in the preparation of our novel adhesive
compositions.
Two test sample compositions, J and K, were made by blending two
mixtures which, except for a varied salt catalyst, had the same
formulation.
The respective formulations of said compositions were as
follows:
__________________________________________________________________________
Sample and Amount (grams) Ingredient J K
__________________________________________________________________________
Part A: Water 450 450 Corn Starch 400 400 ViAc:NMA copolymer (as in
Ex.I) 400 400 Boric Acid 2 2 Part B: A commercial colloidal clay 20
20 Corn Starch 40 40 Urea-formaldehyde resin (high 40 40 molecular
weight) Aluminum Sulfate 12 -- Aluminum Chloride -- 12
__________________________________________________________________________
The two above described compositions were then utilized in the
manufacturing of a series of single faced, A-fluted corrugated
boards, at machine speeds ranging from 100 to 400 fpm, in a manner
similar to that outlined in Example I. The resulting corrugated
boards were held for 24 hours under ambient conditions and,
thereafter, duplicate samples taken from each board were subjected
to the "Straight" Wet Pin Test described in Example I.
The viscosity, the varied machine speeds utilized, and the
respective test results are presented below in Table No. 5.
Table No. 5 ______________________________________ Sample Viscosity
(cps) Machine Speed (fpm) Wet Pin
______________________________________ J 450 100 38 200 37 300 40
400 36 K 400 100 57 200 65 300 65 400 65
______________________________________
The data presented above clearly shows that various other acid salt
catslysts may be utilized in the same manner as the zirconium
oxychloride and the chromium nitrate, in the preparation of the
present novel adhesive compositions.
EXAMPLE XIII
This example illustrates the usefulness of our novel adhesive
compositions in the preparation of corrugated boards using a medium
and a liner which have been previously treated with a
rigid-when-wet coating composition.
In this case, two A-flute, single face boards were prepared, at
varied machine speeds, in a manner similar to that employed in
Example I, except herein the corrugating medium and the liner had
been impregnated with a resole phenolic resin system of the type
disclosed in U.S. Pat. No. 3,697,365. The formulation of the
adhesive composition utilized to bond said medium to said liner was
the same as used in Exmple I. The resulting corrugated boards were
set aside under ambient conditions for 24 hours and were then
tested as described below.
Six 2 .times. 4 inch samples were taken from each board. One of
said samples was subjected to the Pin Adhesion Test described
hereinabove. The remaining five samples were each handled in a
special manner prior to being similarly tested. The particular
manner in which each of said five samples were further conditioned
and the respective test results for all six samples are set forth
in the table below.
Table No. 6
__________________________________________________________________________
Test Results 1 hour 1 hour 1 hour immersion immersion Machine Dry
immersion 30 min. after after Speed (As in at 30 min. 5 mins. 5
mins. at (fpm) is) water* 400.degree. F. at 400.degree. F. at
250.degree. F. 250.degree. F.
__________________________________________________________________________
100 99 30 79 42 119 39 250 119 23 74 47 --** --
__________________________________________________________________________
*All immersions were made in water maintained at 77.degree. F.
**Not tested.
The data presented above clearly illustrate that the novel adhesive
compositions of this invention are useful in the manufacturing of
corrugated boards of which the medium and liner have been treated
with a conventional type thermosetting, rigid-when-wet mixture. The
outstanding water resistance and thermal stability of the adhesive
composition are reflected by the good to excellent results
reported.
EXAMPLE XIV
This example illustrates the high degree of water resistance and
excellent thermal stability of a polyvinyl acetate based adhesive
composition typical of this invention.
In this case, corn starch was used in combination with a
urea-formaldehyde thermosetting resin, and aluminum chloride was
employed as the acid salt catalyst.
The formulation of the test sample herein was as follows:
______________________________________ Ingredients Amount (grams)
______________________________________ Water 450 Corn starch 430
Boric acid 2 Polyvinyl acetate (aqueous emulsion about 40% 400
solids) A commercially available colloidal clay 30 A commercially
available high MW urea- 40 formaldehyde resin Aluminum chloride 12
______________________________________
The above described ingredients were thoroughly stirred into a
homogeneous composition which had a viscosity of 250 cps as
determined by the method described in Example I. Said composition
was then utilized in the manufacturing of a series of standard
type, A-fluted corrugated boards, at machine speeds ranging from
100 to 400 fpm, in a manner similar to that outlined in Example I.
The resulting corrugated boards were stored under ambient
conditions for 24 hours and thereafter tested by means of the
standard Pin Adhesion test described in Example I. The varied
speeds at which the corrugator was run and the corresponding test
results are set forth below.
Table No. 7
__________________________________________________________________________
Description of Tests and Results
__________________________________________________________________________
"Oven Cured" Wet Pin: Wet Pin: tested after being immersed in water
for Machine tested after 1 1 hour following cure in oven set at
Speed hour immersion 400.degree. F. for period indicated below.
(fpm) in water (77.degree. F.) 3 min. 5 min. 10 min. 15 min.
__________________________________________________________________________
100 45 56 61 59 68 200 43 50 54 58 63 300 37 42 49 48 54 400 36 38
45 55 50
__________________________________________________________________________
The data presented above clearly indicate that polyvinyl acetate
based adhesive compositions prepared in accordance with this
invention yield bonds which are water-resistant and thermally
stable.
When a series of single face, A-fluted corrugated boards prepared
with a polyvinyl acetate based adhesive composition similar to that
described above, but having polyvinyl alcohol as a thickener
instead of the colloidal clay, were tested, the results were
comparable to those set forth above.
EXAMPLE XV
This example illustrates the usefulness of an interpolymer in the
preparation of an adhesive composition, in accordance with this
invention.
In this case, a butyl acrylate based terpolymer was utilized in the
preparation of an adhesive composition in the following manner:
A thickener mixture was first prepared by slowly dissolving 179.22
grms of polyvinyl alcohol in a solution comprised of 76.56 grams of
a commercially available colloidal clay and 1.16 grams of a
defoaming agent in 1711.0 grams of water. Then 405.0 grams of the
resulting mixture was admixed with a slurry having the following
formulation:
__________________________________________________________________________
Ingredient Amount (grams)
__________________________________________________________________________
Water 1122.0 Corn starch 1020.0 A polyvinyl alcohol stabilized
terpolymer of 1003.0 butyl acrylate, vinyl acetate, and
N-isobutoxymethylol acrylamide (75.0:25.0:1.5 wt. ratio) Dimethyl
hydroxyethyl triazone (Protorez 1850) 120.2 Chromic nitrate 51.0
__________________________________________________________________________
Said terpolymer was synthesized by a conventional means of emulsion
polymerization. Said adhesive composition was then utilized in
preparation of a series of four single face corrugated boards, at
varied speeds up to 350 fpm, as described in Example I. Upon being
allowed to equilibrate at ambient conditions over a period of 24
hours, the bonds of said boards were tested by methods employed in
Example II, except that the combined extended curing step and
thermal stability evaluation of the "Oven Cured" Wet Pin test
involved placing the samples in an oven set at 350.degree. F., for
20 minutes. The varied machine speeds and the corresponding
averages of the results obtained from duplicate samples are set
forth below.
Table No. 8
__________________________________________________________________________
Test Results Machine Speed (fpm) Dry Pin Wet Pin "Oven Cured" Wet
Pin
__________________________________________________________________________
50 52.5 9.0 13.5 150 119.0 7.5 22.0 250 134.0 16.5 31.5 350 112.0
22.5 27.0
__________________________________________________________________________
The data summarized above clearly indicates that butyl acrylate
based interpolymers are readily useful in the preparation of the
adhesive compositions of this invention.
EXAMPLE XVI
The procedure outlined in Example XV was repeated to make an
adhesive composition using the same amount of a terpolymer
essentially consisting of butyl acrylate, acrylonitrile, and
N-methylol acrylamide (95:5:3 wt. ratio). Portions of this adhesive
composition were utilized in the manufacturing of a series of three
single face corrugated boards at varied machine speeds up to 250
fpm. The adhesive bonds of said boards exhibited water resistance
and thermal stability properties comparable to those of the test
sample in Example XV.
Summarizing, our invention provides corrugating adhesive
compositions which yield bonds capable of exhibiting outstanding
water resistance and thermal stability. Furthermore, our invention
provides adhesive compositions which are useful in the preparation
of rigid-when-wet, as well as conventional corrugated boxboard. As
used herein, "outstanding" water resistance and thermal stability
means that the laminate bonded with the cured adhesive will not
exhibit a tendency to separate when immersed in water either before
or after being exposed to temperatures between about 250.degree.
and 450.degree. F. for a considerable period, yielding a wet or dry
bond strength substantially in excess of commercial standards.
Variations in procedures and proportions may be made without
departing from the scope of this invention which is defined by the
following claims.
* * * * *